[R-sig-Geo] image background for spplot of gridded data

[Waichler, Scott R]

I was told, among other things, to look for previous messages by Oscar that would explain how to do this.  Here is Oscar's solution that I found to work for the case where you want to plot two rasters that have different extents.  In my case, gmap is a satellite image obtained with RgoogleMaps, and z are the results I want to plot over the background image.  I made the alpha values of z less than 1 so that the background image would show through.

library(rasterVis)
levelplot(z~x*y) + 
layer_(grid.raster(gmap, y=latCenter, width=width, height=height, default.units='native'))

Scott Waichler